CN113891678A

CN113891678A - Tracking catheter based on model of impedance tracking field

Info

Publication number: CN113891678A
Application number: CN202080038518.8A
Authority: CN
Inventors: 托比亚斯·施罗德
Original assignee: Boston Scientific Scimed Inc
Current assignee: Boston Scientific Scimed Inc
Priority date: 2019-03-22
Filing date: 2020-03-19
Publication date: 2022-01-04
Also published as: US11596471B2; US20200297413A1; WO2020197935A1; EP3941347A1

Abstract

A system for tracking a catheter within a patient. The system includes a plurality of surface electrodes and a surface patch attached to the patient, and a processor coupled to the plurality of surface electrodes and the surface patch. A processor determines a location of at least one of the plurality of surface electrodes; storing a location of at least one of the surface patch and the plurality of surface electrodes; determining a three-dimensional shell shape corresponding to a portion of a patient; determining a model of an impedance tracking field in at least a portion of the three-dimensional shell shape; injecting a current through one or more of the plurality of surface electrodes; fitting the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter; and providing therapy to the patient based on the position of the catheter.

Description

Tracking catheter based on model of impedance tracking field

Cross Reference to Related Applications

This application claims priority to provisional patent application No. 62/822,351 filed on 3/22/2019, which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to systems and methods for tracking a catheter within a patient, and more particularly, to systems and methods for tracking a catheter without first mapping a region of interest within a patient. The present disclosure also relates to systems and methods for tracking a catheter based on a model that fits measured voltages to an impedance tracking field in a region of interest within a patient.

Background

Some mapping systems provide an impedance tracking function for navigating a catheter within a patient. Generally, in these systems, the impedance tracking function relies on injecting current into the electrodes such that an electric field is generated within the patient. To determine the location of the catheter, the electric field distribution in a region of interest (e.g., the interior of the heart) is mapped using a dedicated mapping catheter. This mapping catheter may be a magnetically tracked mapping catheter that measures impedance tracking fields in the region of interest. The magnetically tracked position of the catheter and the field voltage measured by the catheter are used to create a map of the region of interest. The system stores the collected data in a map, which may include one or more look-up tables of measured field voltages. To navigate the catheter in the region of interest, the field voltage is measured by the catheter and compared to one or more look-up tables.

Some systems do not use the mapped impedance tracking field information, but instead rely on pairs of electrodes each placed on opposite sides of the patient's body. The electrode pairs are positioned to generate fields that are approximately orthogonal to each other such that catheter tracking employs orthogonal fields.

In other systems, x-ray fluoroscopy is used to navigate a catheter within a patient. In x-ray fluoroscopy, successive x-ray images are produced and displayed on a monitor by passing an x-ray beam through the body. In some procedures, fluoroscopy may be combined with impedance tracking methods (such as those described above) to navigate a catheter within a patient.

The need to first create a map of the impedance tracking field in the region of interest and/or the use of x-ray fluoroscopy presents disadvantages. One drawback is that the catheter is navigated within the patient in a less complex procedure that is not worth the time and money spent mapping the region of interest. Another disadvantage is that the patient is exposed to excessive x-rays during the fluoroscopy procedure, wherein the doctor and/or medical staff wishes to reduce the exposure to x-rays.

Moreover, systems employing orthogonal electrode pairs add cost and complexity to the procedure and equipment, as additional electrode surface patches and corresponding system connections are required. Furthermore, exploiting field orthogonality only provides limited accuracy, since the exact electrode position is still unknown.

Disclosure of Invention

In example 1, a system for tracking a catheter in a patient includes a plurality of surface electrodes attached to the patient, a surface patch attached to the patient, and a processor coupled to the plurality of surface electrodes and the surface patch. The processor is configured to: determining a position of at least one of the plurality of surface electrodes; storing a location of the surface patch and a location of at least one of the plurality of surface electrodes; determining a three-dimensional shell shape corresponding to a portion of a patient; determining a model of an impedance tracking field in at least a portion of the three-dimensional shell shape; injecting a current through one or more of the plurality of surface electrodes to create an electric field within the patient; fitting the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient; and providing therapy to the patient based on the position of the catheter.

In example 2, the system of example 1, wherein the plurality of surface electrodes are a plurality of electrocardiogram electrodes attached to the patient.

In example 3, the system according to any of examples 1 and 2, wherein the surface patch is a surface back patch comprising a magnetic tracking system that provides location information about a location of the surface back patch attached to the back of the patient.

In example 4, the system of any of examples 1 to 3, comprising a stylus operable to track a position of the stylus, wherein the processor is coupled to the stylus and configured to determine a position of at least one of the plurality of surface electrodes by receiving position information from the stylus when the stylus contacts the electrode.

In example 5, the system of any of examples 1 to 4, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an ovoid shape, a location of the surface patch and a location of at least one of the plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and an anatomical landmark within the patient.

In example 6, the system of any of examples 1 to 5, wherein the processor is configured to determine the model of the impedance tracking field based on an estimate of the electromagnetic tissue property of the patient based on at least one of: a constant gradient across the patient, an estimate of the location of an organ within the patient, and electrical impedance tomography of the patient.

In example 7, the system of any of examples 1 to 6, wherein the processor is configured to refine the model of the (refine) impedance tracking field based on at least one of the measured voltage from the tracking catheter and the magnetically obtained position of the tracking catheter within the patient.

In example 8, the system of any of examples 1 to 7, wherein the processor is configured to provide respiratory gating (respiratory gating) to fit the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient.

In example 9, a method of tracking a catheter includes: determining, by a processor, a location of at least one of a plurality of surface electrodes attached to a patient; storing, by a processor, a location of at least one of the plurality of surface electrodes; storing, by a processor, a location of a surface patch attached to a patient; determining, by a processor, a three-dimensional shell shape corresponding to a portion of a patient; determining, by a processor, a model of an impedance tracking field in at least a portion of a three-dimensional shell shape; injecting, by a processor, a current into one or more of a plurality of surface electrodes to create an electric field within a patient; fitting, by the processor, the measured voltage from the catheter to a model of the impedance tracking field to track a position of the catheter within the patient; and providing, by the processor, a therapy to the patient based on the position of the catheter.

In example 10, the method of example 9, wherein storing the location of the surface patch includes obtaining location information from a tracking system in the surface back patch, and wherein determining the location of the at least one of the plurality of surface electrodes includes determining, by the processor, the location of the at least one of the plurality of electrocardiogram electrodes attached to the patient.

In example 11, the method of any one of examples 9 and 10, including receiving location information from a stylus capable of tracking a location of the stylus when determining the location of at least one of the plurality of surface electrodes.

In example 12, the method of example 11, wherein determining, by the processor, the three-dimensional shell shape comprises determining the three-dimensional shell shape based on one or more of: the location of the surface patch and the location of at least one of the plurality of surface electrodes determined from the location information received from the stylus, the location of the plurality of points on the surface of the patient determined from the location information received from the stylus, and the location of the anatomical landmark within the patient determined from the location information received from the stylus.

In example 13, the method of any of examples 9 to 12, wherein determining, by the processor, the three-dimensional shell shape comprises determining the three-dimensional shell shape based on one or more of: an ovoid shape, a location of the surface patch and a location of at least one of the plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and an anatomical landmark within the patient.

In example 14, the method of any of examples 9 to 13, wherein determining, by the processor, the model of the impedance tracking field in at least a portion of the three-dimensional shell shape includes determining the model based on an estimate of electromagnetic tissue properties of the patient, the estimate of electromagnetic tissue properties including one or more of: a constant gradient across the patient, an estimate of the location of an organ within the patient, electrical impedance tomography of the patient (such as electrical impedance tomography of the patient based on sensed impedance between electrodes), measured voltages from the tracking catheter, and a magnetically obtained location of the tracking catheter within the patient.

In example 15, the method of any of examples 9 to 14, wherein fitting, by the processor, the measured voltage from the catheter to the model of the impedance tracking field includes respiratory gating.

In example 16, a system for tracking a catheter in a patient includes a plurality of surface electrodes attached to the patient, a surface patch attached to the patient, and a processor coupled to the plurality of surface electrodes and the surface patch. The processor is configured to: determining a position of at least one of the plurality of surface electrodes; storing a location of the surface patch and a location of at least one of the plurality of surface electrodes; determining a three-dimensional shell shape corresponding to a portion of a patient; determining a model of an impedance tracking field in at least a portion of the three-dimensional shell shape; injecting a current through one or more of the plurality of surface electrodes to create an electric field within the patient; fitting the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient; and providing therapy to the patient based on the position of the catheter.

In example 17, the system of example 16, wherein the plurality of surface electrodes are a plurality of electrocardiogram electrodes attached to the patient.

In example 18, the system of example 16, wherein the surface patch is a surface back patch including a magnetic tracking system that provides location information regarding a location of the surface back patch attached to the back of the patient.

In example 19, the system of example 16, comprising a stylus operable to track a position of the stylus, wherein the processor is coupled to the stylus and configured to determine the position of the at least one of the plurality of surface electrodes by receiving position information from the stylus.

In example 20, the system of example 16, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an ovoid shape, a location of the surface patch and a location of at least one of the plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and an anatomical landmark within the patient.

In example 21, the system of example 16, wherein the processor is configured to determine a model of the impedance tracking field based on an estimate of the electromagnetic tissue property of the patient.

In example 22, the system of example 21, wherein the estimation of the electromagnetic tissue property of the patient is based on at least one of: a constant gradient across the patient, an estimate of the location of an organ within the patient, and electrical impedance tomography of the patient.

In example 23, the system of example 21, wherein the processor is configured to refine the model of the impedance tracking field based on at least one of the measured voltage from the tracking catheter and the magnetically obtained position of the tracking catheter within the patient.

In example 24, the system of example 16, wherein the processor is configured to receive a system reference voltage for obtaining the measured voltage from the catheter, the system reference voltage received from at least one of: a reference catheter within the patient, a reference patch attached to the patient, one or more of the plurality of surface electrodes, and a surface patch.

In example 25, the system of example 16, wherein the processor is configured to provide respiratory gating to fit the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient.

In example 26, a system for tracking a catheter within a patient, comprising: a plurality of electrocardiogram electrodes attached to a patient; a surface back patch including a magnetic tracking system that provides positional information about a location of the surface back patch on the back of the patient; a stylus enabling the stylus to track a position of the stylus; and a processor coupled to the plurality of surface electrodes, the surface backside patch, and the stylus. The processor is configured to: determining positions of a plurality of electrocardiogram electrodes according to position information obtained from a stylus pen; determining the position of the surface back patch according to the position information from the surface back patch; storing the positions of the plurality of electrocardiogram electrodes and the positions of the surface back patches; based on the locations of the plurality of electrocardiogram electrodes and the location of the surface back patch; determining a three-dimensional shell shape corresponding to a portion of a patient based on the locations of the plurality of electrocardiogram electrodes and the location of the surface back patch; determining a model of an impedance tracking field in at least a portion of the three-dimensional shell shape; injecting a current through one or more of the plurality of electrocardiographic electrodes to create an electric field in the patient; fitting the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient; and providing therapy to the patient based on the position of the catheter.

In example 27, the system of example 26, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an oval shape, the location of multiple points on the surface of the patient, and anatomical landmarks within the patient.

In example 28, the system of example 26, wherein the processor is configured to determine the model of the impedance tracking field based on an estimate of electromagnetic tissue of the patient, the estimate of the electromagnetic tissue property comprising one or more of: a constant gradient across the patient, an estimate of the location of an organ within the patient, and electrical impedance tomography of the patient (such as electrical impedance tomography of the patient using impedance information measured with a plurality of surface electrodes and surface patches).

In example 29, the system of example 26, wherein the processor is configured to receive a system reference voltage obtained from one or more of: a reference catheter within the patient, a reference patch attached to the patient, one or more of the plurality of surface electrodes, and a surface patch.

In example 30, a method of tracking a catheter in a patient includes: determining, by a processor, a location of at least one of a plurality of surface electrodes attached to a patient; storing, by a processor, a location of at least one of the plurality of surface electrodes; storing, by a processor, a location of a surface patch attached to a patient; determining, by a processor, a three-dimensional shell shape corresponding to a portion of a patient; determining, by a processor, a model of an impedance tracking field in at least a portion of a three-dimensional shell shape; injecting, by a processor, a current into one or more of a plurality of surface electrodes to create an electric field within a patient; fitting, by the processor, the measured voltage from the catheter to a model of the impedance tracking field to track a position of the catheter within the patient; and providing, by the processor, a therapy to the patient based on the position of the catheter.

In example 31, the method of example 30, wherein storing the location of the surface patch includes obtaining location information from a tracking system in the surface back patch, and wherein determining the location of the at least one of the plurality of surface electrodes includes determining, by the processor, the location of the at least one of the plurality of electrocardiogram electrodes attached to the patient.

In example 32, the method of example 30, comprising receiving location information from a stylus capable of tracking a location of the stylus when determining the location of the at least one of the plurality of surface electrodes.

In example 33, the method of example 30, wherein determining, by the processor, the three-dimensional shell shape comprises determining the three-dimensional shell shape based on one or more of: an ovoid shape, a location of the surface patch and a location of at least one of the plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and an anatomical landmark within the patient.

In example 34, the method of example 30, wherein determining, by the processor, the model of the impedance tracking field in at least a portion of the three-dimensional shell shape includes determining the model based on an estimate of an electromagnetic tissue property of the patient, the estimate of the electromagnetic tissue property including one or more of: a constant gradient across the patient, an estimate of the location of an organ within the patient, electrical impedance tomography of the patient, measured voltages from a tracking catheter, and a magnetically obtained position of the tracking catheter within the patient.

In example 35, the method of example 30, wherein the processor is configured to provide respiratory gating while obtaining the measured voltage from the catheter.

While multiple embodiments are disclosed, still other embodiments of the present disclosure will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the disclosure. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not as restrictive.

Drawings

Fig. 1 is a schematic diagram illustrating a system for tracking a catheter (or multiple catheters) within a patient according to an embodiment of the present disclosure.

FIG. 2 is a diagram illustrating one example of a stylus that can be used to track the position of the stylus in a system according to an embodiment of the present disclosure.

Fig. 3A is a diagram illustrating a plurality of surface electrodes attached to a patient and a three-dimensional housing shape depicted in phantom corresponding to a portion of the patient according to an embodiment of the disclosure.

Fig. 3B is a diagram illustrating a surface patch attached to a patient according to an embodiment of the present disclosure.

Fig. 4 is a diagram illustrating a computational grid of voltages and complex permittivities according to an embodiment of the present disclosure.

Fig. 5 is a diagram illustrating a finite difference model at a body surface (two-dimensional) according to an embodiment of the present disclosure.

Fig. 6 is a diagram illustrating a catheter in a patient's heart and a three-dimensional housing shape affixed to the patient according to an embodiment of the present disclosure.

Fig. 7 is a method of tracking a catheter in a patient according to an embodiment of the present disclosure.

Detailed Description

Fig. 1 is a diagram illustrating a system 20 for tracking a catheter 22 (or multiple catheters 22) within a patient 24 according to an embodiment of the present disclosure. The system 20 is configured to track a catheter 22 in a region of interest (e.g., the heart) within a patient 24 without first mapping the region of interest. System 20 is configured to track catheter 22 based on a model that measures field voltages within patient 24 with catheter 22 and fits the measured field voltages to impedance tracking fields in a region of interest of patient 24. In an embodiment, system 20 is used to insert a catheter (such as catheter 22) into a heart or heart chamber of patient 24.

The system 20 includes a processor 26, a pointer or stylus 28, a plurality of surface electrodes 30, a surface patch 32, the catheter 22, and, in at least some embodiments, a magnet 34. In an embodiment, the plurality of surface electrodes 30 are a plurality of Electrocardiogram (ECG) electrodes attached to the patient 24. In some embodiments, surface patch 32 is a surface back patch that is attached to the back of patient 24.

A plurality of surface electrodes 30 and surface patches 32 are attached to the patient 24 and are coupled to the processor 26 by conductive paths (not shown for clarity). The stylus 28 is coupled to the processor 26 by a conductive path 38, and the magnet 34 is coupled to the processor 26 by a conductive path 40. The conduit 22 is coupled to the processor 26 by a conductive path 42. In an embodiment, one or more of the processor 26, the stylus 28, the plurality of surface electrodes 30, the surface patch 32, the catheter 22, and the magnet 34 may be coupled to the processor 26 by wireless communication.

Enabling the stylus 28 to be used to track the position of the stylus 28 in the system 20. In an embodiment, the stylus 28 is enabled for tracking the position of the stylus 28 relative to one or more of: a table on which the patient 24 lies and a magnet 34 or another part of the system 20. In some embodiments, the stylus 28 includes a magnetic field tracking system such that the stylus 28 can be used to magnetically track the position of the stylus 28 in the magnetic field of the magnet 34. In some embodiments, the magnet 34 is an electromagnet, and in some embodiments, the magnet 34 is controlled by the processor 26.

The processor 26 is configured to receive position information from the stylus 28 to determine the position of the plurality of surface electrodes 30. In an embodiment, the processor 26 is configured to activate the magnet 34, and the stylus 28 is configured to provide the position information to the processor 26. In some embodiments, each of the plurality of surface electrodes 30 is contacted by the stylus 28, and when the stylus 28 is brought into contact with each of the plurality of surface electrodes 30, the stylus 28 provides the processor with positional information of the stylus 28. In an embodiment, the processor 26 determines the location of the stylus 28 and the contacted surface electrode 30 and stores the location of the contacted surface electrode 30.

The processor 26 is also configured to store the location of the surface patch 32. In an embodiment, the surface patch 32 is enabled for use in tracking the position of the surface patch 32 in the system 20. In an embodiment, the surface patch 32 is enabled for tracking the position of the surface patch 32 relative to one or more of: a table on which the patient 24 lies and a magnet 34 or another part of the system 20. In some embodiments, the surface patches 32 include a magnetic field tracking system such that the surface patches 32 can be used to magnetically track the position of the surface patches 32 in the magnetic field of the magnet 34. In an embodiment, the processor 26 is configured to activate the magnet 34, and the surface patch 32 is configured to provide the position information to the processor 26. In some embodiments, the surface patch 32 is a surface back patch that includes a magnetic tracking system that provides the processor 26 with location information regarding the location of the surface back patch attached to the back of the patient 24.

In some embodiments, the location of the surface patch 32 is obtained using the stylus 28, as described above with respect to the plurality of surface electrodes 30. In an embodiment, the stylus 28 contacts the surface patch 32 and the processor 26 receives location information from the stylus 28 when the stylus contacts the surface patch 32, wherein the processor 26 determines and stores the location of the surface patch 32.

The processor 26 determines a three-dimensional shell shape corresponding to a portion of the patient 24. In some embodiments, the processor 26 determines a three-dimensional shell shape corresponding to a region of interest within the patient 24. In some embodiments, the processor 26 determines a three-dimensional shell shape corresponding to a chest region within the patient 24. In an embodiment, the processor 26 is configured to determine the three-dimensional housing shape based on one or more of the oval shape, the locations of the surface patch 32 and the plurality of surface electrodes 30 on the patient 24, the locations of the plurality of other points on the surface of the patient 24, and anatomical landmarks within the patient 24.

The processor 26 determines a model of the impedance tracking field in at least a portion of this three-dimensional shell shape based on the estimate of the electromagnetic tissue properties of the patient 24. In an embodiment, the estimation of the electromagnetic tissue properties of the patient 24 is based on at least one of: a constant gradient across the patient 24, an estimate of the location of an organ within the patient 24, and Electrical Impedance Tomography (EIT) imaging of the patient 24.

In some embodiments, the processor 26 is configured to refine the model of the impedance tracking field based on the position information received from the tracking catheter within the patient 24 and the measured field voltages. The tracking catheter measures the field voltage of an impedance tracking field generated within the patient 24, such as by injecting current through the plurality of surface electrodes 30 and the patient 24 into the surface patch 32. The processor 32 fits a model of the impedance tracking field to the measured voltages to refine the model. In some embodiments, the tracking catheter is catheter 22. In some embodiments, tracking the catheter includes a magnetic tracking system that provides position information about the position of the tracking catheter and the measured field voltages to the processor 26.

To track a catheter (such as catheter 22) in a region of interest within the patient 24, the processor 26 is configured to inject electrical current through one or more of the plurality of surface electrodes 30 to create an electric field in the patient 24. This electric field is an impedance tracking field used to track the position of catheter 22. In operation, catheter 22 measures the field voltage of the impedance tracking field, and processor 26 fits the measured field voltage from catheter 22 to a model of the impedance tracking field and determines the position of catheter 22 in patient 24.

Also, processor 26 receives a system reference voltage for obtaining the measured field voltage from catheter 22. In an embodiment, the system reference voltage is received from at least one of a reference catheter within the body of the patient 24, a reference patch attached to the patient 24, one or more of the plurality of surface electrodes 30, and a surface patch 32. Moreover, in some embodiments, processor 26 is configured to provide respiratory gating to fit the measured field voltage from catheter 22 to a model of the impedance tracking field to determine the location of catheter 22 within patient 24.

The catheter 22 is a movable catheter 22 having one or more spatially distributed electrodes. The catheter 22 may be used to perform various medical procedures, such as cardiac mapping and/or medical treatments including ablation, such as Radio Frequency (RF) ablation and/or cryoablation. Catheter 22 is used by medical personnel and/or a physician based on the position of catheter 22 within patient 24 as determined by processor 26.

In some embodiments, catheter 22 is equipped with various types of electrodes configured to perform various functions. For example, catheter 22 may include at least one pair of Current Injection Electrodes (CIE) configured to inject current into the medium in which catheter 22 is disposed. The catheter 22 may also include a plurality of potential measuring electrodes (PEMs) configured to measure the potential resulting from the current injected by the current injection electrodes. In some embodiments, the PME is used for cardiac mapping. In some embodiments, the relative position of the plurality of catheters 22 disposed in the heart or cardiac chambers of the heart of the patient 24 is determined based on measured field voltages obtained by the PME on the catheters 22. In some embodiments, the position of catheter 22 may be determined relative to the surface of an organ (such as the heart of patient 24).

Further with respect to system 20, processor 26 is configured to provide and actually provide the functionality of system 20. The processor 26 is a processor-based device that includes one or more computers, microprocessors, and/or other types of processor-based devices suitable for a variety of applications. The processor 26 may include volatile and/or non-volatile memory elements 44 and peripheral devices to implement input/output functions. The peripheral devices may include, for example, a CD-ROM drive, a floppy disk drive, and/or a network connection for downloading relevant content to the processor 26. Such peripheral devices may also be used to download software containing computer instructions to implement the operation of the processor 26 and to download software implemented programs to perform the operation of the system 20. Processor 26 may be implemented on a single or multiple processor-based platforms capable of performing the functions of system 20. Additionally, one or more of the processes performed by processor 26 may be implemented using processing hardware, such as a Digital Signal Processor (DSP), a Field Programmable Gate Array (FPGA), a mixed signal integrated circuit, and an Application Specific Integrated Circuit (ASIC).

In an embodiment, processor 26 includes an electronics module 46 coupled to one or more of stylus 28, plurality of surface electrodes 30, surface patch 32, and catheter 22 to receive signals from and provide signals to one or more of stylus 28, plurality of surface electrodes 30, surface patch 32, and catheter 22. The electronics module 46 may include a signal generation module for injecting electrical current through the surface electrodes 30 into a region of interest, such as a heart chamber. Electronics module 46 may also include a signal acquisition module for measuring electrical potentials through surface electrodes 30 and/or through electrodes (e.g., PMEs) of catheter 22. The electronics module 46 may also include a signal acquisition module for receiving location information from the stylus 28 and/or location information from the surface patch 32. In an embodiment, electronics module 46 is used to one or more of sample, sense, filter and amplify the received signal.

The electronics module 46 may be implemented using analog or digital electronics, or a combination of both. In some embodiments, the electronic module 46 is implemented using integrated components on a dedicated printed circuit board. In some embodiments, at least some of the signal conditioning tasks are performed by one or more of a Central Processing Unit (CPU), FPGA, and DSP. In some embodiments, electronics module 46 is implemented using analog hardware with signal processing capabilities enhanced by CPU, FPGA and DSP devices.

As shown in FIG. 1, the system 20 also includes input/output devices 48, such as a mouse and keyboard, a printer 50, and a display device 52, which may include a touch screen. Moreover, the system 20 includes a storage device 54 for storing data collected by the processor 26. The input/output device 48, printer 50, display device 52, and storage device 54 are each communicatively coupled to the processor 26, such as by wired connections or wirelessly.

The processor 26 may access one or more input devices for obtaining input data and one or more output devices for communicating output data. In an embodiment, the input/output devices 48 include one or more of the following: random Access Memory (RAM), Redundant Array of Independent Disks (RAID), floppy disk drives, Compact Disk (CD) drives, DVD drives, diskettes, internal hard drives, external hard drives, memory sticks, and other storage devices accessible by the processor 26, wherein such preceding examples are not exhaustive and are intended to be illustrative and not limiting.

The systems and methods described herein are not limited to one hardware/software configuration. The systems and methods may be implemented in hardware or a combination of hardware and software, and/or may be implemented by commercially available modules, applications and devices. Where the systems and methods described herein are based, at least in part, on the use of a computer, microprocessor, and/or other computing device, the systems and methods may be implemented in one or more computer programs, where a computer program may be understood to include one or more processor-executable instructions. The computer programs may be executed on processor 26 and may be stored on one or more storage media readable by processor 26, such as memory element 44 and storage device 54.

Furthermore, the computer program can be implemented using one or more high-level procedural or object-oriented programming languages to communicate with a computer system, and/or the computer program can be implemented in assembly or machine language. The language may be compiled or interpreted. The device and/or computer system integrated with the processor 26 may include, for example, a personal computer, a workstation (e.g., Sun, HP), a Personal Digital Assistant (PDA), a handheld device such as a cellular telephone, laptop computer, handheld device, or another device capable of being integrated with the processor. Accordingly, the devices provided herein are not exhaustive and are provided for purposes of illustration and not limitation.

Moreover, throughout this disclosure, references to "microprocessor" and "processor" or "the microprocessor" and "the processor" may be understood to include one or more microprocessors and/or processors that may communicate in a stand-alone and/or distributed environment, and thus may be configured to communicate with other processors via wired or wireless communication. Additionally, unless otherwise specified, references to memory may include one or more processor-readable and accessible memory elements and/or components that may be internal to a processor device, and/or external to a processor device, and that may be accessed via a wired or wireless network using various communication protocols, and that may be arranged to include a combination of external and internal memory devices, where such memory may be contiguous and/or partitioned based on application, unless otherwise specified. Thus, references to a database may be understood to include one or more memory associations, where such references may include commercially available database products (e.g., SQL, Informix, Oracle) and/or proprietary databases, and may also include other structures for associating memories such as links, queues, graphs, trees, where such structures are provided for illustration and not limitation.

FIG. 2 is a diagram illustrating one example of a stylus 28 that can be used to track the position of the stylus 28 in the system 20, according to an embodiment of the present disclosure. In an embodiment, the stylus 28 is configured for determining six degrees of freedom in a six degree of freedom electromagnetic tracking system. Also, in an embodiment, the stylus 28 is at least one of non-sterile and reusable.

In the example embodiment described herein, the stylus 28 includes three magnetic tracking coils 60a-60c for determining the position of the stylus 28 in the magnetic tracking field generated by the magnet 34. In other example embodiments, the stylus 28 includes only two magnetic coils for determining six degrees of freedom. In some example embodiments, the stylus 28 includes only two magnetic coils for determining six degrees of freedom, where the two magnetic coils are not orthogonal or parallel to each other.

In this example, three magnetic coils 60a-60c are positioned at or toward the distal end 62 of the stylus 28. The three magnetic coils 60a-60c are oriented orthogonal to one another such that one coil is positioned in each of the three x-y-z directions. Each of the three magnetic tracking coils 60a-60c is electrically coupled to the processor 26 in a conductive path 38, such as by a separate wire. The stylus 28 and connecting conductive path 38 are long enough to reach each of the surface electrodes 30 while the magnetic tracking coils 60a-60c remain within the magnetic tracking field created by the magnet 34. In some embodiments, the three magnetic coils 60a-60c are not oriented orthogonal to each other. Moreover, in other embodiments, the stylus 28 includes less than three magnetic coils 60a-60c or more than three magnetic coils 60a-60c, wherein the less than three magnetic coils and the more than three magnetic coils may or may not be orthogonal to each other.

In operation, the processor 26 activates the magnet 34 to generate the magnetic tracking field(s), and each of the three magnetic tracking coils 60a-60c transmits a signal corresponding to the magnetic tracking field(s) back to the processor 26. The processor 26 receives the signals and determines the position of the stylus 28 in the magnetic tracking field and relative to the system 20, such as relative to one or more of: a table on which the patient 24 lies and a magnet 34 or another part of the system 20.

In some embodiments, the stylus 28 includes a distal tip 64 that may be depressed, such as by a contact electrode, and the stylus 28 transmits a signal to the processor 26 in response to the distal tip 64 being depressed. The signal may be used by the processor 26 to indicate that the signal currently being transmitted by the magnetic tracking coils 60a-60c is to be used to determine the position of the stylus 28. Also, in some embodiments, the distal tip 64 of the stylus 28 may be depressed, and the stylus 28 transmits one or more separate signals to the processor 26 in response to the distal tip 64 being depressed and the signals from the magnetic tracking coils 60a-60c to be used to determine the position of the stylus 28. In other embodiments, the stylus 28 may be otherwise configured to indicate that the stylus 28 has been brought into contact with an object, such as an electrode, such as by using capacitance or inductance.

Fig. 3A and 3B are diagrams illustrating a plurality of surface electrodes 30 and surface patches 32 attached to a patient 24, according to an embodiment of the present disclosure.

Fig. 3A is a diagram illustrating a plurality of surface electrodes 30 attached to a patient 24 and a three-dimensional shell shape 66 depicted in phantom corresponding to a portion of the patient 24, according to an embodiment of the present disclosure. In this example, the plurality of surface electrodes 30 are a plurality of ECG electrodes 30 attached to the patient 24. In an embodiment, plurality of ECG electrodes 30 includes 10 electrodes. In other embodiments, plurality of ECG electrodes 30 includes more than 10 electrodes, such as 12 or more electrodes. In some embodiments, plurality of ECG electrodes 30 includes less than 10 electrodes.

To obtain the location of the plurality of ECG electrodes 30 attached to the patient 24, at least one of the plurality of ECG electrodes 30 is contacted by the stylus 28, and the stylus 28 provides signals from the three magnetic tracking coils 60a-60c to the processor 26. The stylus 28 is contacted to at least one of the plurality of ECG electrodes 30 by one or more medical personnel, such as a physician, nurse, and/or mapping specialist. In an embodiment, stylus 28 also provides a separate signal to one of the plurality of ECG electrodes 30 indicating that stylus 28 has been contacted, and processor 26 uses this signal to indicate that the signal transmitted by magnetic tracking coils 60a-60c is to be used to determine the position of stylus 28. In some embodiments, the location of other electrodes of the plurality of ECG electrodes 30 is calculated or determined from the location of at least one of the plurality of ECG electrodes 30 as determined above.

In an embodiment, to obtain the location of each of the plurality of ECG electrodes 30 attached to patient 24, each of the plurality of ECG electrodes 30 is contacted by stylus 28, and when each of the plurality of ECG electrodes 30 is contacted, stylus 28 provides signals from three magnetic tracking coils 60a-60c to processor 26. In an embodiment, when each of the plurality of ECG electrodes 30 is contacted, stylus 28 provides a separate signal to one of the plurality of ECG electrodes 30 indicating that stylus 28 is being contacted.

Processor 26 receives signals from stylus 28 and determines the location of stylus 28 and contacted ECG electrode 30. Processor 26 then stores the location of stylus 28 and contacted ECG electrode 30.

Fig. 3B is a diagram illustrating a surface patch 32 attached to a patient 24, according to an embodiment of the present disclosure. In this example, the surface patch 32 is a back patch 32 that is attached to the back of the patient 24. The back patch 32 is configured for magnetically tracking the position of the back patch 32 in the magnetic tracking field of the magnet 34. In an embodiment, the back patch 32 is configured for magnetically tracking 5 or 6 degrees of freedom in the magnetic tracking field of the magnet 34. In some embodiments, the back patch 32 includes one magnetic tracking coil for determining five degrees of freedom. In some embodiments, the back patch 32 includes two magnetic tracking coils for determining six degrees of freedom. In some embodiments, the back patch 32 includes three magnetic tracking coils for determining six degrees of freedom. In some embodiments, the back patch 32 includes two magnetic coils for defining six degrees of freedom, wherein the two magnetic coils are not orthogonal or parallel to each other. In some embodiments, the back patch 32 includes three magnetic tracking coils similar to the three magnetic tracking coils 60a-60c described above for the stylus 28.

Enabling the back patch 32 to be used to track the position of the back patch 32 relative to one or more of: a table on which the patient 24 lies and a magnet 34 or another part of the system 20. In some embodiments, the two or three magnetic coils are not oriented orthogonal to each other. Also, in other embodiments, the back patch 32 includes less than three magnetic coils or more than three magnetic coils.

To obtain the position of back patch 32, processor 26 activates magnet 34 and back patch 32 provides a signal from the magnetic coil to provide position information to processor 26. The processor 26 receives signals from the back patch 32 and determines the location of the back patch 32. The processor 26 then stores the location of the back patch 32.

Also, in some embodiments, changes in the position and/or orientation of back patch 32 represent shifts in the position of patient 24. These shifts in the position of patient 24 are detected using back patch 32 and used by processor 26 to compensate, for example, for the tracked position or orientation of catheter 22. Where the back patch 32 is used as an impedance tracking spatial reference. Thus, if the patient 24 moves relative to the magnetic tracking reference frame, the movement is detected and a mathematical correction is applied such that the impedance tracked and/or magnetically tracked catheter 22 remains in the same coordinate system.

In some embodiments, the location of back patch 32 is obtained using stylus 28, as described above with respect to multiple ECG electrodes 30. In an embodiment, the stylus 28 is brought into contact with the backplate 32, and the processor 26 receives position information from the stylus 28 when the stylus contacts the backplate 32. The processor 26 then determines the location of the stylus 28 and the back patch 32 and stores the location of the stylus 28 and the back patch 32.

After the location of at least one or both of the plurality of ECG electrodes 30 and back patch 32 is known and recorded, processor 26 determines a three-dimensional housing shape 66 and a mathematical model of the electric field passing through three-dimensional housing shape 66. In the present example, the three-dimensional shell shape 66 corresponds to a chest region within the patient 24 that includes the heart of the patient 24.

The processor 26 determines a three-dimensional shell shape 66. In some embodiments, the processor 26 determines the three-dimensional shell shape 66 to be a simple oval shape with little or no scaling. In some embodiments, processor 26 determines three-dimensional shell shape 66 using an optimization algorithm to scale the oval shape to a best fit inside the location of at least one or all of the plurality of ECG electrodes 30 and back patch 32.

In some embodiments, processor 26 fits three-dimensional housing shape 66 to the locations of at least one or all of plurality of ECG electrodes 30 and back patch 32. In some embodiments, processor 26 uses an optimization algorithm to determine three-dimensional housing shape 66 to obtain a best fit to the location of at least one or all of the plurality of ECG electrodes 30 and back patch 32. In some embodiments, processor 26 determines three-dimensional housing shape 66 using a three-dimensional fitting algorithm to fit three-dimensional housing shape 66 to at least one or all of plurality of ECG electrodes 30 and the location of back patch 32.

In some embodiments, stylus 28 is used to scribe lines along the surface of patient 24, wherein processor 26 records the locations of the scribed lines and fits three-dimensional housing shape 66 to the locations of the scribed lines and the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32. In some embodiments, processor 26 fits three-dimensional shell shape 66 to the locations of the scribed points and at least one or all of the plurality of ECG electrodes 30 and the location of back patch 32 using one or more of an optimization algorithm and a three-dimensional fitting algorithm for obtaining a best fit.

In some embodiments, anatomical landmarks are identified in or on patient 24, such as by EIT or using stylus 28, and processor 26 fits three-dimensional shell shape 66 to the anatomical landmarks and the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32. In some embodiments, stylus 28 is used to identify anatomical landmarks in patient 24, wherein processor 26 records the locations of the anatomical landmarks and fits a three-dimensional housing shape 66 to the locations of the anatomical landmarks and the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32. In some embodiments, processor 26 fits three-dimensional shell shape 66 to anatomical landmarks and the locations of at least one or all of the plurality of ECG electrodes 30 and back patch 32 using one or more of an optimization algorithm and a three-dimensional fitting algorithm for obtaining a best fit.

Next, the processor 26 records the location of the plurality of ECG electrodes 30 as current injection points and determines a model of the impedance tracking field in the three-dimensional shell shape 66 (which corresponds to the chest region of the patient 24, including the heart of the patient 24). The processor 26 determines a model of the impedance tracking field based on an estimate of electromagnetic tissue properties in a region of interest of the patient 24 (the chest in this example).

Electromagnetic tissue properties have an effect on the voltage distribution inside the body. Parameters such as conductivity σ (r) and permittivity ∈ (r) differ between tissue types, see table 1.

Table 1: 13027Hz [4].

Assumptions of uniform tissue properties can be used, depending on the tracking field model accuracy requirements. Alternatively, the model may contain different tissue regions based on a shape atlas of common human anatomy data. The atlas is then scaled based on the approximated chest shape. In a further limitation, a dedicated drive pattern of the available surface electrodes 30 may provide input data to the optimization routine in a similar way to EIT to adjust the tissue type distribution.

Furthermore, the relevant parameter to be included in the model is the impedance of the electrode-skin interface. This impedance can be determined by driving the current from one ECG electrode 30 and sinking it to the adjacent ECG electrode 30. Analyzing the resulting voltage drop may provide an estimate of the skin-electrode interface and underlying tissue impedance.

In an embodiment, the estimation of the electromagnetic tissue properties of the patient 24 is based on a constant gradient across the chest of the patient 24, without taking into account different tissue properties. In some embodiments, the estimation of the electromagnetic tissue properties of the patient 24 is based on an estimation of the location of organs (such as the heart and lungs) in the chest of the patient 24, where the organs scale internally as the three-dimensional shell shape 66 scales externally. In some embodiments, the estimation of the electromagnetic tissue properties of the patient 24 is based on EIT imaging of the patient 24.

In an embodiment, the distal tip 64 of the stylus 28 includes a stylus tip end electrode in electrical contact with the skin of the patient 24. The stylus tip end electrode is configured as a voltage sensing and current driving electrode. In an embodiment, the stylus 28 transmits one or more separate signals to the processor 26 in response to the stylus tip electrode contacting the skin of the patient 24. These signals are used to determine the position of the stylus 28.

In an embodiment, the user contacts multiple skin surface points of patient 24 around the anatomical region of interest, and the system records the location of the stylus tip end electrode and the impedance between the stylus tip end electrode and various electrodes (such as ECG electrode 30 and/or back patch 32). The stylus tip electrode position information and impedance information complements the position and impedance information of the electrodes, such as ECG electrode 30 and back patch 32. This leads to a better adapted mathematical problem when solving anatomical distributions of non-uniform complex permittivity, such as when using EIT algorithms.

In an embodiment, to facilitate electrical contact between the tip electrode of the indicator tip and the skin of the patient 24, the tip electrode of the indicator tip is provided with an absorbent material impregnated with a conductive gel. Moreover, in some embodiments, the additional surface electrodes are attached to the patient 24 at locations that facilitate accounting for the anatomical distribution of the non-uniform complex permittivity through, for example, EIT algorithms. The additional surface electrodes are not permanently connected to the system. Rather, impedance measurements made with these additional electrodes are only performed when they are contacted by the stylus 28, so that when contacted, the system acquires additional electrode positions based on the magnetically tracked position of the stylus 28, and simultaneously acquires electrical impedance measurements.

The processor 26 determines a model of the impedance tracking field in the three-dimensional shell shape 66, which corresponds to the chest region of the patient 24, as follows:

the poisson equation establishes a relationship between local voltage (v (r)) and charge density. Magnetic induction effects are ignored because the impedance tracking field frequency is low enough to assume quasi-static model behavior. Under these assumptions, the poisson equation in its generalized form is given as follows:

where ρ represents the complex-valued charge density and ∈ c is the complex permittivity according to:

since we expect the dielectric constant and current density to be non-uniform throughout the thoracic cavity, ec (r) is a function of position r.

Alternatively, if the model accuracy requirements are less stringent, a simpler approximation is a uniform distribution of ec (r). In this case, the generalized poisson equation reduces to:

in the forward solution, a relatively simple method of solving for (1) and (3) is a finite difference method. As the name implies, it approximates the derivatives by finite differences in the discretized model.

Using homogeneous tissue properties, to implement (3), the three-point approximation of the second derivative of v (r) with respect to the x coordinate is:

where n, m, and k are indices of the discretized computational domain, and h is the grid spacing. Applying to equation (3) and assuming equal grid spacing in all three directions provides:

solving V (n, m, k) to obtain

Approximations using a large number of neighboring points are also available.

In the generalized poisson equation, the representation of equation (6) must consider the local e c (r) distribution in the case of varying electromagnetic tissue properties. In this scenario, the solution evaluates finite differences between voltage samples weighted by the average complex permittivity between them. From a mathematical derivation similar to the two-dimensional case, the three-dimensional finite difference solution for the generalized poisson distribution of v (r) is (compared to fig. 4):

wherein

Note that the grids of e c and V are offset by half the grid spacing (fig. 4), i.e., e c (n, m, k) ∈ c (xn + h/2, zm + h/2, zk + h/2). This offset simplifies the mathematical solution and allows the calculation of the electric field along the boundary of c.

The boundary conditions of the numerical optimization problem are the voltages measured at ECG electrodes 30 and back patch 32, and the fact that the in vitro conductivity is zero. These scalar measurements and values are referred to as Dirichlet boundary conditions (see fig. 5).

If an Inferior Vena Cava (IVC) catheter is used, further boundary conditions may be applied to its measurements. However, the IVC catheter position is not known a priori. To apply its measurements as a boundary condition, the catheter position may be fixed to a certain point in the atlas-based anatomical model. This approach is acceptable as long as it is understood that the impedance field approximation provides valid tracking information strictly only with respect to its atlas-based model.

In some embodiments, the processor 26 is configured to refine the model of the impedance tracking field based on the position information received from the tracking catheter within the patient 24 and the measured field voltages. Current is injected through a plurality of ECG electrodes 30 into dorsal patch 32, generating an impedance tracking field in patient 24. The tracking catheter measures the field voltage of the impedance tracking field and provides the measured voltage to the processor 26. The processor 26 fits a model of the impedance tracking field to the measured voltages to refine the model. In some embodiments, the tracking catheter is catheter 22. In some embodiments, a tracking catheter is inserted into one of the IVC and the Superior Vena Cava (SVC). In some embodiments, tracking the catheter includes a magnetic tracking system that provides position information about the position of the tracking catheter and the measured field voltages to the processor 26.

Fig. 6 is a diagram illustrating catheter 22 in heart 68 of patient 24 and three-dimensional housing shape 66 affixed to patient 24, according to an embodiment of the present disclosure. As shown in fig. 3A and 3B, ECG electrodes 30 and a dorsal patch 32 (not shown in fig. 6 for clarity) are attached to patient 24. Furthermore, a reference patch 70 is attached to the patient 24 to provide a reference voltage for making measurements of the impedance tracking field within the patient 24 using electrodes 72 on the catheter 22.

Catheter 22 is a movable catheter having one or more spatially distributed electrodes 72 at or near the distal end of catheter 22. In some embodiments, catheter 22 is used to perform a treatment. In some embodiments, the catheter 22 is used to perform ablation, such as RF ablation and/or cryogenic ablation. In some embodiments, catheter 22 is used to perform diagnostics. In some embodiments, the catheter 22 is used to perform cardiac mapping. In some embodiments, the catheter 22 is inserted into the coronary sinus of the patient 24. In some embodiments, catheter 22 is used to refine the model of the impedance tracking field based on the position of catheter 22 and the measured field voltages received from electrodes 72 of catheter 22.

The catheter 22 may be equipped with various types of electrodes 72. In some embodiments, the catheter 22 includes one or more ablation electrodes 72 for performing ablation. In some embodiments, conduit 22 includes at least one pair of CIE configured to inject current into the medium in which conduit 22 is disposed. In some embodiments, catheter 22 includes a PME for measuring the voltage or potential of the impedance tracking field within patient 24. In some embodiments, catheter 22 includes a PME for measuring the voltage or potential generated by the CIE injected current. In some embodiments, the PME is used for cardiac mapping.

Reference patch 70 provides a reference voltage to processor 26, which is used by processor 26 as a reference for the measured voltage from catheter 22. In other embodiments, the processor 26 receives a reference voltage from another source. In some embodiments, the processor 26 receives the system reference voltage from a reference catheter within the patient 24 (such as a reference catheter disposed in the IVC or SVC). In some embodiments, processor 26 receives a system reference voltage from one or more of the plurality of surface electrodes 30. In some embodiments, the processor 26 receives a system reference voltage from the surface patch 32.

In operation, processor 26 injects current through one or more of the plurality of ECG electrodes 30 into back patch 32. This creates an electric field in the patient 24, which is an impedance tracking field used to track the position of the catheter 22. With catheter 22 inserted into patient 24, such as into heart 68, electrodes 72 on catheter 22 measure field voltages of the impedance tracking field and provide the measured voltages or potentials to processor 26. The processor 26 receives the measured field voltage referenced to the reference voltage from the reference patch 70 and signal conditions the measured voltage as needed.

In some embodiments, the processor 26 performs pre-processing on the measured voltage signals, wherein the pre-processing includes one or more of noise reduction and filtering.

Processor 26 then fits the measured field voltage from catheter 22 to a model of the impedance tracking field. In an embodiment, the processor 26 matches the measured field voltage to a model of the impedance tracking field. In some embodiments, the processor 26 uses an optimization algorithm to match the measured field voltage to a model of the impedance tracking field, and the processor 26 obtains a best fit of the measured field voltage to the model.

After fitting the measured field voltages from the catheter 22 to the model of the impedance tracking field, the processor 26 determines the location of the catheter 22 within the patient 24, such as in the heart 68 of the patient 24. Based on the position of the catheter 22 within the patient 24 as determined by the processor 26, medical personnel and/or physicians use the catheter 26 to perform procedures, such as diagnostic, mapping, or therapeutic procedures, including ablation.

In an embodiment, the processor 26 is configured to detect artifacts and reduce artifacts in the measured field voltage. In some embodiments, the processor 26 is configured to provide noise reduction for the measured field voltages. In some embodiments, the processor 26 is configured to provide respiratory gating to obtain the measured field voltage. In respiratory gating, the processor 26 measures the field voltage of the impedance tracking field using the catheter 22 during the same period of the respiratory cycle as the patient 24 breathes in and out of air. In some embodiments, the processor 26 measures the field voltage as the air exits the patient, as there is more time for the measurement to take place as the air exits the patient 24.

Fig. 7 is a method of tracking a catheter, such as catheter 22, within a patient 24 according to an embodiment of the present disclosure. The method is performed by the system 20. In other embodiments, the method may be performed by or by a different system.

The method includes determining, by the processor 26, a location of at least one of the plurality of surface electrodes 30 attached to the patient 24 at 100. Wherein, in some embodiments, the plurality of surface electrodes 30 is a plurality of ECG electrodes 30. Further, in some embodiments, the method includes determining, by the processor 26, a location of each of the plurality of surface electrodes 30 attached to the patient 24. In some embodiments, the processor 26 determines the location of other electrodes of the plurality of surface electrodes 30 based on one or more locations of at least one of the plurality of surface electrodes 30.

Further, in some embodiments, the method includes receiving location information from a stylus, such as stylus 28. The stylus is enabled for tracking the position of the stylus and providing position information to the processor 26 when the stylus is brought into contact with an electrode of the plurality of surface electrodes 30, the surface patch 32 and/or another point on the patient 24.

The method includes storing, by the processor 26, a location of at least one of the plurality of surface electrodes 30 at 102, and storing, by the processor 26, a location of a surface patch 32 attached to the patient 24 at 104. These locations may be stored in an internal memory of the processor 26 or in a memory external to the processor 26. In some embodiments, the method includes storing, by the processor 26, a location of each of the plurality of surface electrodes 30. In some embodiments, the method includes storing, by processor 26, a location of each of the plurality of ECG electrodes 30. Also, in some embodiments, the method includes storing the location of the back patch 32.

Next, the method includes determining, by the processor 26, a three-dimensional shell shape 66 corresponding to a portion of the patient 26 at 106. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on an oval shape, which may include scaling the oval shape to fit the locations of the surface electrode 30 and the backside patch 32. In some embodiments, determining the three-dimensional housing shape 66 includes determining the three-dimensional housing shape 66 based on the location of the surface patch 32 and the location of one or more of the plurality of surface electrodes 30. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on the location of other points on the patient 24. In some embodiments, determining the three-dimensional shell shape 66 includes determining the three-dimensional shell shape 66 based on anatomical landmarks within the patient 24, such as anatomical landmarks obtained from an atlas model or from imaging (such as EIT imaging, etc.).

The method includes determining, by the processor 26, a model of an impedance tracking field in a portion of the three-dimensional shell shape 66 at 108. In some embodiments, the method includes determining the model based on an estimate of electromagnetic tissue properties of the patient 24. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, including a constant gradient across the patient 24. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, including estimates of the location of organs in the patient 24. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, the estimates based on EIT imaging, or the like. In some embodiments, the method includes determining the model based on estimates of electromagnetic tissue properties of the patient 24, including measured field voltages from the tracking catheter and magnetically obtained positions of the tracking catheter within the patient 24.

In tracking the catheter, at 110, the method includes injecting, by the processor 26, a current into the surface patch 32 through one or more of the plurality of surface electrodes 30 to create an electric field within the patient 24. This electric field is an impedance tracking field that is subsequently detected and measured by electrodes on a catheter inserted into the patient 24, such as electrodes 72 on catheter 22.

At 112, the method includes fitting, by the processor 26, the field voltage measured by the catheter to a model of the impedance tracking field to track the position of the catheter within the patient 24. In some embodiments, the processor 26 matches the measured field voltage to a model of the impedance tracking field. In some embodiments, the processor 26 uses an optimization algorithm to match the measured field voltage to a model of the impedance tracking field, and the processor 26 obtains a best fit of the measured field voltage to the model.

In an embodiment, after fitting the measured field voltages from the catheter to the model of the impedance tracking field, the processor 26 determines the location of the catheter within the patient 24, such as in the heart 68 of the patient 24. Based on the position of the catheter within the patient 24, medical personnel and/or physicians use the catheter to perform procedures, such as diagnostic, mapping, and/or therapeutic procedures, such as therapeutic procedures including ablation.

At 114, the method includes providing, by the processor 26, therapy to the patient based on the catheter position determined by the processor 26.

Moreover, in some embodiments, the method includes detecting and reducing artifacts in the measured voltages, such as by providing noise reduction to the measured field voltages and/or providing respiratory gating while obtaining the measured field voltages.

The systems and methods described herein reduce or eliminate the need to first create a map of the impedance tracking field in a region of interest within the patient 24. This reduces the cost of performing the procedure so that a less complex procedure can be performed that does not require the time or money required to map the region of interest. Moreover, the systems and methods described herein do not use fluoroscopy, such that exposure to excess x-rays is reduced.

Various modifications and additions may be made to the exemplary embodiments discussed without departing from the scope of the present disclosure. For example, although the embodiments described above refer to particular features, the scope of the present disclosure also includes embodiments having different combinations of features and embodiments that do not include all of the features described above.

Claims

1. A system for tracking a catheter within a patient, comprising:

a plurality of surface electrodes attached to the patient;

a surface patch attached to the patient; and

a processor coupled to the plurality of surface electrodes and the surface patch, the processor configured to:

determining a location of at least one surface electrode of the plurality of surface electrodes;

storing a location of the surface patch and a location of at least one of the plurality of surface electrodes;

determining a three-dimensional shell shape corresponding to a portion of the patient;

determining a model of an impedance tracking field in at least a portion of the three-dimensional shell shape;

injecting a current through one or more of the plurality of surface electrodes to create an electric field within the patient;

fitting the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient; and

providing therapy to the patient based on the position of the catheter.

2. The system of claim 1, wherein the plurality of surface electrodes are a plurality of electrocardiogram electrodes attached to the patient.

3. The system according to any one of claims 1 and 2, wherein the surface patch is a surface back patch comprising a magnetic tracking system that provides location information regarding a location of the surface back patch attached to the back of the patient.

4. The system of any of claims 1 to 3, comprising:

a stylus operable to track the stylus position, wherein the processor is coupled to the stylus and configured to determine a position of at least one of the plurality of surface electrodes by receiving position information from the stylus.

5. The system of any one of claims 1 to 4, wherein the processor is configured to determine the three-dimensional shell shape based on one or more of: an oval shape, a location of the surface patch and a location of at least one of the plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and an anatomical landmark within the patient.

6. The system of any one of claims 1 to 5, wherein the processor is configured to determine the model of the impedance tracking field based on an estimate of the electromagnetic tissue properties of the patient based on at least one of: a constant gradient across the patient, an estimate of a location of an organ within the patient, and electrical impedance tomography of the patient.

7. The system of any one of claims 1 to 6, wherein the processor is configured to refine the model of the impedance tracking field based on at least one of a measured voltage from a tracking catheter and a magnetically obtained position of the tracking catheter within the patient.

8. The system of any one of claims 1 to 7, wherein the processor is configured to provide respiratory gating to fit the measured voltage from the catheter to a model of the impedance tracking field to determine the location of the catheter within the patient.

9. A method of tracking a catheter, comprising:

determining, by a processor, a location of at least one surface electrode of a plurality of surface electrodes attached to a patient;

storing, by the processor, a location of at least one surface electrode of the plurality of surface electrodes;

storing, by the processor, a location of a surface patch attached to the patient;

determining, by the processor, a three-dimensional shell shape corresponding to a portion of the patient;

determining, by the processor, a model of an impedance tracking field in at least a portion of the three-dimensional shell shape;

injecting, by the processor, a current into one or more of the plurality of surface electrodes to create an electric field within the patient;

fitting, by the processor, the measured voltage from the catheter to a model of the impedance tracking field to track a position of the catheter within the patient; and

providing, by the processor, a therapy to the patient based on the position of the catheter.

10. The method of claim 9, wherein storing the location of the surface patch comprises obtaining location information from a tracking system in the surface back patch, and wherein determining the location of at least one of the plurality of surface electrodes comprises determining, by the processor, the location of at least one of a plurality of electrocardiogram electrodes attached to the patient.

11. The method according to any one of claims 9 and 10, comprising receiving position information from a stylus capable of tracking a position of the stylus when determining the position of at least one of the plurality of surface electrodes.

12. The method of claim 11, wherein determining, by the processor, the three-dimensional shell shape comprises determining the three-dimensional shell shape based on one or more of: a location of the surface patch and a location of at least one of the plurality of surface electrodes determined from the location information received from the stylus, a location of a plurality of points on the surface of the patient determined from the location information received from the stylus, and a location of an anatomical landmark within the patient determined from the location information received from the stylus.

13. The method of any of claims 9-12, wherein determining, by the processor, the three-dimensional shell shape comprises determining the three-dimensional shell shape based on one or more of: an oval shape, a location of the surface patch and a location of at least one of the plurality of surface electrodes, a location of a plurality of points on a surface of the patient, and an anatomical landmark within the patient.

14. The method of any of claims 9 to 13, wherein determining, by the processor, a model of the impedance tracking field in at least a portion of the three-dimensional shell shape comprises determining the model based on an estimate of electromagnetic tissue properties of the patient comprising one or more of: a constant gradient across the patient, an estimate of a location of an organ within the patient, electrical impedance tomography of the patient, a measured voltage from a tracking catheter, and a magnetically obtained location of the tracking catheter within the patient.

15. The method of any of claims 9 to 14, wherein fitting, by the processor, the measured voltage from the catheter to the model of the impedance tracking field comprises respiratory gating.